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 TB FlX v3 by ToneBoosters is a Virtual Effect Audio Plugin for macOS and Windows. It functions as a VST Plugin and an Audio Units Plugin.
Product TB FlX v3
Developer ToneBoosters
Price (MSRP)
10-plugin bundle for € 49,-
Type / Tags Compressor Dynamics EQDynamics and EQEqualizer
Plug-in, App & Soundware Format(s)
Operating System Availability
Download Released
Downloads Released
Downloads Released
Miscellaneous Information
Copy ProtectionKey File

Equalizer sections and filter types

TB FlX ("Flex") combines equalization and dynamics processing in one go. It works just as most equalizers; it has 6 filter sections with lots of controls to modify their effect on the spectrum. More than 30 filter types are currently supported, which include classic analog peaking and shelving filters and resonating low- and high-pass filters. Besides these conventional filter types, some not-so-common or entirely novel filters are available as well:

  • Bell-shape filters that have a flatter top than analog filters, to give a more natural sound;
  • Non-resonating shelving filters to allow for steeper filter slopes;
  • Gaussian filters, because these filters have the shortest possible group delay;
  • Gammatone filters, because they closely mimic the frequency analysis of our hearing system;
  • Linear and logarithmically-spaced harmonic filters, for creative effects;
  • Brick-wall highpass, lowpass, and bandpass filters;
  • Analog resonating highpass and lowpass filters (order between 1 and 16);
  • Analog bandpass filter;
  • Spectral balance filter;
  • and several more.

In the unlikely case that you want to create a filter shape that is different from any of the included ones, TB FlX supports a so-called 'auto node link' mode. In this mode, the filter shapes will be automatically constructed such, that their combined effect will give a smooth, interpolated curve through all nodes that were configured as 'auto node link' filter.

Each filter section has its own 'amount' control to modify how much of that filter is actually applied to the audio signal. Furthermore, the filter can be applied in stereo, left only, right only, mid only or side only channels.

Linear phase or minimum phase?

We have closely followed the sometimes intense debates on minimum phase and linear phase equalizers, and the pros and cons of each of them. We understand that you appreciate the surgical editing precision of linear phase, and the snappy, accurate time response with minimum pre-ringing of minimum phase. Wouldn't it be great if these benefits could be combined in one algorithm, without the cons?

TB Flx has the potential to solve the minimum vs linear phase debacle for once and for all by introducing 'auto phase'. The phase response of the equalizer is dynamically adjusted to give the best of both worlds, adapted to the input signal and the desired equalizer curve.

Dynamics processing without limits

Each filter section also has a dedicated dynamics processing (compressor) stage. This means that a filter response can become more or less active depending on the input signal level. The compressor input/output curve is configured by dragging nodes in an input/output graph. This way, the input/output curve can be configured beyond what is possible with conventional compressors using threshold and ratio controls. Expansion, downward compression, upward compression, positive or negative ratios, parallel compression, New-York style compression (via the 'amount' control) are all easy to set up, and can be configured for each filter section independently. Of course you can set the attack and release times, and an auto-release (AR) function is supplied as well.

The level detector of each compressor section also has some innovative features. Besides being able to respond to stereo level changes, the level detector side chain can also operate on mid only, side only, left or right only, and even on the side-over-mid ratio.

Putting it all together

All user-accessible and internal parameters are interpolated automatically with maximum precision, using 4 times oversampling. This gives ultra-smooth, zipper-noise free behaviour for no-compromise, professional-grade output quality. And did we mention the integrated DC-reject filter (DCF)?


  • More than 100 parameters to shape the sound in a clean and simple interface.
  • 6 filter sections with many controls to modify their behavior;
  • More than 30 filter types, including a unique 'auto node link' filter type.
  • 3-node dynamics processing editor for each filter section.
  • Manual and auto-release (AR) option.
  • Integrated output spectrum analyzer with zoom functionality.
  • Unique, innovative auto-phase filter mode for high-resolution transient response.
  • Based on the VST 2.4 specification to allow compatibility with virtually all host programs.
Latest User Reviews Average user rating of 5.00 from 4 reviews

Reviewed By Sycopation
May 8, 2016

This is by far the cheapest multiband compressor with sidechain that I could find, and it works great. Very transparent. Everything else out there is over $100. ToneBoosters offers similar products for a fraction of what their competitors charge.

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Reviewed By FarleyCZ
April 12, 2016

Imma be quick on thisone. This is hands down the best dynamic EQ I've used. Don't get me wrong. I've tried pretty much all the major ones and they are awesome, but I always get lost in that "range" parameter. Fix draws you classic dynamic curve for each EQ filter. This makes it super intuitive to use. It also sounds great. I've been able to save some pretty sh***y recordings with it. Can't believe it costs only 19 Euros. It's an absolute steal.

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Reviewed By SnappyDee
August 5, 2014

This is an outstanding product. Just as an EQ it earns its place in any studio - 30 different filter types which all sound just as they should. There are also AutoLink filters where you simply place the points on the frequency graph to 'draw' the filter curve - so you get the best of both worlds. On top of that you can also define a compression curve for each filter to give you dynamic EQ. In fact it's more flexible than just compression - you can draw almost any kind of curve for some really interesting effects. I think some people may overlook this plugin because the flx name doesn't really hint at the dynamic EQ possibilites. The potential really is endless with this little gem and it looks fantastic too. It doesn't sound good or bad - it just sounds 'right' - it does its job without drawing attention to itself - exactly how it should be.

ToneBoosters is a great company - don't be fooled by the low prices - their business model is based on selling the highest quality plugins at very affordable prices. They're also very fair - you can download and try full versions of the plugins before you buy. I own this and the TrackEssentials package which is also great value.

Update 21 Dec 2014 - I've been using this for a while now. The possibilites really are endless, but one very useful thing I've just discovered is how great this works as a de-esser. There are two versions of this plugin (both included in the price) - you need to use the FLX4 plugin that has a sidechain input. I use an EQ to broadly filter out everything except the problem frequencies, then I route that to the sidechain input on TB Flx4 and use it to drive the compressor curves of the filters - then you can fine tune the flx filter (s) to sculpt out the problem frequencies. It's not like multiband de-essing because you can partially overlap the filters, and use different compression curves and attack/release on each one, so it's much more powerful. Most singers have a distinct 'ess' profile, so it's easy and quick to fine tune the filters for each artist.

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Reviewed By Proxima4
February 25, 2014

I bought this plugin after trying other similar pitch/auto tracing eq's but found Jeroens approach much easier to get on with.

It's really easy to use from everything such as multi band compression or expansion, surgical attenuation of problem frequencies and transient re-cycled rhythms.

Jeroen has a professional academic background in DSP and has found a model for his business that has always supported the end user and the business model.

If your in any doubt about this ad other plugins, then don't, try the demo and see how easy it is to add interesting and useful effect to your tracks.

His interesting and yet simple approach to multiband dynamics is likely to bring fresh perspective to this plugins design.

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Discussion: Active
29 April 2015 at 5:34pm

This is a great plugin. Absolutely.

But My complaint is working frequency range (50Hz~something). I hope next update has extended frequency range.

13 May 2016 at 7:32pm

TDR Nova is free and is great too...

Mustang Martigan
Mustang Martigan
16 October 2017 at 1:41pm

Anyone know if there's an AAX version of this plugin? I want to use it in Pro Tools. I don't understand why they decided to change the software to be solely compatible with AAX format.


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TB FlX v3

Average user rating of 5.00 from 4 reviews

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